docs: def raise_for_old_graph(graph):
      """Raise an ImportVersionWarning if the BEL graph was produced by a legacy version of PyBEL.
  
      :raises ImportVersionWarning: If the BEL graph was produced by a legacy version of PyBEL
      """
      graph_version = tokenize_version(graph.pybel_version)
      if graph_version < PYBEL_MINIMUM_IMPORT_VERSION:
          raise ImportVersionWarning(graph_version, PYBEL_MINIMUM_IMPORT_VERSION)